When connecting metal components to CFK components, as is the case with a CFK-metal hybrid construction, certain protective measures must be taken in order to prevent galvanic corrosion or contact corrosion. Galvanic corrosion can endanger the structural integrity of a construction. Beginning with the reduction of load-bearing cross sections, the metal component can ultimately be completely destroyed. Therefore, galvanic corrosion must be prevented and the effect of the protective measures must be checked, for example by means of regular inspections of the CFK-metal connection.
With galvanic corrosion, different galvanic voltage potentials between a CFK component and a metal component, interacting with an electrolyte, lead to corrosion.
The metal component, which for example consists of aluminium or an aluminium alloy, in this case forms the anode, while the CFK component, or its carbon portion, forms the cathode. Moisture, or condensation water, which for example forms in the bilge of a fuselage, in this case acts as electrolyte. In the bilge, a highly aggressive electrolyte consisting of water, and all liquids which are to be encountered in the human environment, are customarily to be found in abundant quantities. If the connection consisting of metal component and CFK component comes into contact with the electrolyte, then a current flows. In doing so, positive metal atoms of the metal component (cations) migrate to the negative pole of the cathode or of the CFK component. The anode or the metal component slowly decomposes as a result of this cation flow.
By one of the two components, in most cases the CFK component, being electrically insulated to prevent such galvanic corrosion, is known to the applicant. This takes place by means of encapsulating, for example with a GFK material which in the galvanic series is “neutral” compared with metal components and CFK components. By means of encapsulating, the component is reliably separated from its electrolytic environmental surroundings, wherein the cathode and the electrode (anode) are separated from each other so that no current can flow. As a result, the occurrence of galvanic corrosion can be prevented.
Encapsulating of a CFK component or of a metal component with GFK materials, however, has the disadvantage that it is very complicated and cost-intensive, especially if the components have a complex shape. During encapsulating, the corresponding component, inclusive of all its lips, spatial corners, ends and edges, must be encapsulated in an electrically insulating manner. The usefulness of encapsulating an element, therefore, is dependent upon the individual case and must be individually checked. In this case, the additional costs of encapsulating very easily compensate the cost advantage which is actually aimed at with a CFK-metal hybrid construction. That means, the advantages which lie in the material combination of CFK and metal cannot be utilized, or not fully utilized.
To isolate the electron conductor between the electrodes, for example by a glass fibre mat being laid between the CFK component and the metal component in order to electrically separate the parts from each other, is known to the applicant. This method, however, has the disadvantage that it does not suffice if the two components are additionally connected to each other via connecting elements, such as rivets, bolts or screws consisting of a metal material or CFK material.